The subject invention relates to film-forming resins capable of low-temperature cure. More particularly, the invention relates to film-forming resins capable of curing through alkoxy silane groups and coating compositions containing the film-forming resin and, optionally, polyols.
In recent years, the coatings industry has become increasingly interested in low-temperature cure coating compositions. These compositions must be capable of being applied by conventional techniques such as spraying, dipping, roll-coating, brushing, etc., yet be capable of curing at a low temperature, ideally room temperature. Obviously, the primary advantage of these compositions is the lessened energy demands.
The coatings industry has also become interested in low organic solvent-containing coating compositions. Such compositions must also be capable of application by conventional techniques. These coating compositions present several advantages including high film build per application, economy of materials, especially in organic solvents which are lost to ambient surroundings, lessened concerns about pollution problems caused by the evaporation of organic solvents and also energy savings since less air needs to be heated to evaporate the solvents in a curing oven. Additionally, the organic solvents themselves have been in short supply.
Much work has been expended in the coatings industry to formulate coating compositions which contain a low organic solvent content. One area in particular which has received attention has been in the formulation of water-based coating compositions. Water is itself, of course, quite inexpensive and does not pose environmental problems. However, film-forming resins which are capable of being reduced with water are themselves normally water-sensitive and do not provide a film having all the desired characteristics, such as humidity resistance and durability. Still another area of coating technology which has received attention in recent years is the formulation of high solids coating compositions which are of a low viscosity and can be applied by conventional techniques. Such coating compositions can contain what is referred to as reactive diluents. These reactants are capable of thinning the coating composition and then reacting with the film-forming resins after application to a substrate. In effect, the diluent becomes a part of the cured film.
Additionally, there have been formulated coating compositions which are capable of curing at a low temperature and which are low in organic solvent content. However, the known compositions all have one or more drawbacks associated with them. Thus, for example, coating compositions based on alkyd resins are slow to cure to a film and the cured film often does not have particularly good properties. One pack and two pack isocyanate-containing coating compositions suffer from health concerns associated with the isocyanate. Compositions based on a melamine cure also pose a possible health concern due to the liberation of some formaldehyde during the compositions' cure. Epoxy and amine-containing coating compositions have the disadvantage of having to be a two pack system and the films produced from them are often less durable than desired.
While the above areas of endeavor have produced certain desired results, there is still a need for a new generation of coating compositions. These coating compositions would be capable of curing at a low temperature. Additionally, the coating compositions would ideally require low levels of organic solvents, be one-package stable, and be capable of application to a substrate by conventional techniques. There have now been found film-forming resins which are capable of curing at low temperature and which do not require high levels of organic solvents to achieve application viscosity. These film-forming resins can be applied to a substrate and form a durable film. Components such as polyols and crosslinking agents can be blended with the new film-forming resins to provide additional coating characteristics.
As used herein, all percents and ratios are by weight unless otherwise indicated.